Automotive vehicles commonly have seat assemblies that permit the seat back to be selectively reclined, about a horizontal pivot axis, through a range of substantially upright, occupiable positions for selection by the user of a preferred seating position. In the past, rotary recliner mechanisms have proven an effective way to provide such reclining functionality in vehicle seat assemblies. Advantages of known rotary recliner mechanisms include that they are relatively inexpensive to manufacture, that they have their working components substantially enclosed (which lends to their reliability and safety), and that they fit into a relatively small design envelope. One prior art rotary recliner mechanism is disclosed in U.S. Pat. No. 6,336,679 (Smuk et al.), issued Jan. 8, 2002, which is incorporated herein by reference.
Rotary recliners for vehicle seats typically include fixed and mobile plates, with the fixed plate being mounted on the seat cushion and the mobile plate mounted on the seat back. Generally, in the prior art, the mobile plate is rotatably supported by the fixed plate and may be selectively locked relative thereto. Typically, when locked, a toothed gear segment on a pawl that is supported by the fixed plate securely engages a corresponding toothed ring gear provided on the mobile plate.
Notably, in attempting to lock the mobile plate relative to the fixed plate, some prior art rotary recliners have exhibited a certain small range of non-locking conditions. In the result, the seat back may not have locked instantly when the recliner handle was released, instead requiring a slight rearward or forward force to positively lock the recliner. While such rearward and forward forces are generally generated during normal vehicle movement, the free play in the seat back that is inherent during these non-locking conditions of the recliner may be troubling, inter alia, from a safety perspective. Though not essential to an understanding of the present invention, it is generally thought that the non-locking conditions in some prior art rotary recliners may be attributable to the design of the toothed gear segments and the toothed ring gear, and/or to an orientation of the pawls relative to the ring gear. That is, and for example, when the profile of the teeth on the gear segment is identical to that of the teeth on the ring gear, a non-locking (or tip-to-tip) condition may occur. In such situations, the teeth on the ring gear may actually collide with the teeth on the gear segment, thereby preventing the mobile and fixed plates from locking with respect to one another. More specifically, in such tip-to-tip conditions, teeth on opposite outside end portions of the gear segment may engage opposing faces of the corresponding teeth on the ring gear, thereby requiring a slight rearward or forward force on the seat back, and/or a slight rotational force on the mobile plate, to positively lock the recliner. It would be desirable to provide a rotary recliner that has a lower incidence of such non-locking (tip-to-tip) conditions.
One prior art rotary recliner mechanism that has attempted to address the aforementioned problem is disclosed in U.S. Pat. No. 6,749,263 (Peters), issued Jun. 15, 2004. Notably, prior art rotary recliner mechanisms of the general type that are disclosed by the Peters patent have stipulated the essentiality of rotatable eccentric cams which must apply an equilibrium of forces to each of the pawls, through a balanced arrangement of two cam shoulders provided on each of the pawls. Though not essential to an understanding of the present invention, the tolerancing that has heretofore been required between the cams and the cam shoulders of such prior art rotary recliners, in order to effect the purportedly required balanced distribution of forces, has generally been seen to be costly and difficult to achieve in mass-production, with a relatively high incidence of component rejection and/or failure. It would be desirable to provide a rotary recliner that is both highly reliable and cost effective, while at the same time affording a low incidence of non-locking conditions.
Accordingly, it is an object of this invention to obviate or mitigate at least one of the above-mentioned disadvantages of the prior art.